In general, pressure-sensitive adhesive (or PSA; the same applies hereinafter) has characteristics to be in a soft solid (viscoelastic) state in a room temperature range and easily adhere to adherend with some pressure. With the benefit of such properties, PSA is widely used in forms of substrate-supported PSA sheets having a PSA layer at least on one face of the substrate for purposes including fastening and surface protection of various articles and obtaining desirable appearances such as for decorative purposes. Documents disclosing these types of conventional art include Patent Documents 1 and 2.